1. Field of the Invention
This invention relates to a shutter for a camera having a plurality of divided blades and more particularly to a structural arrangement of the shutter which prevents the shutter blades from being damaged by their collision against the edge of a shutter aperture provided in a shutter base plate, etc. when an external force is exerted on the shutter blades while they are operated.
2. Description of the Related Art
A desire to enlarge the range of photographable objects for a camera has recently resulted in the increase of the maximum and flash-synchronizing speeds of shutters. The increase in speed necessitates an increased driving force on the shutter blades and a decreased weight of shutter blades. Hence, the thickness of the shutter blades has become thinner for reduction in weight.
However, as shown in FIG. 11 of the accompanying drawings which shows an example of the prior art, a travelling space for shutter blades is provided jointly by a shutter base plate 1 (positioned on the front side of the shutter or the mirror box side of the camera), a separating plate 5, a cover plate 2, etc. These plates generally require no special arrangement in connection with the reduction in thickness of shutter blades. Therefore, no change has been made in the form of these plates. For example, the shutter base plate 1 is provided simply with a tapered face lh along the edge of a shutter aperture 1a located in the traveling direction of shutter blades.
Further, referring to FIGS. 11 to 15 which show the prior art example, the conventional shutter arrangement includes a leading blade group 3; a trailing blade group 4; a shutter aperture la provided in the shutter base plate 1; a shutter aperture 2a which is provided in the cover plate 2; a shutter aperture 5a provided in the separating plate 5; blade arms 6 and 7; and blade dowels 8.
The structural arrangement of the conventional shutter, however, has the following drawback: The shutter blades having their rigidity lowered by the above stated reduction in thickness would be greatly warped if the shutter is operated while the shutter blades are under an external force which is exerted on them from behind (from the back cover side of the camera) in cases, for example, where the shutter is inadvertently operated with the leader part of a loaded roll of film riding on the shutter blades or with the shutter blades under air pressure while the inside of the back cover of camera is being cleaned by means of a spray. Under such a condition, a slit forming part 4a of the trailing blade group 4 comes to collide with an aperture edge 1c of the shutter base plate 1 which is confronting it and thus would be damaged as shown in FIGS. 12 to 14. More specifically, in the case of a vertical-travel blade type shutter having shutter blades arranged to travel downward from above, the slit forming part 4a of the trailing blade group 4 comes to collide with the aperture edge 1c of the shutter base plate 1 when the shutter blades are traveling, or another part of the trailing blade group 4, such as a part 4b as shown in FIG. 15, comes to collide with another aperture edge of the shutter base plate 1 when the shutter blades are being set for a travel preparing position to cause the shutter blades to be thus damaged there. In the case that the shutter blades are arranged to travel upward from below, a slit forming part of the leading blade group 3 comes to collide with an aperture edge of the shutter base plate 1 when the shutter blades are being set for a travel preparing position or another part of the leading blade group 3 similar to the above stated part 4b comes to collide with an aperture edge of the shutter base plate 1 to damage the shutter when the blades are on their travel.